PROJECT SUMMARY/ABSTRACT Lung aeration is the most critical physiologic task for the preterm infant to achieve after birth for survival. Yet the optimal method of aerating the preterm lung remains unknown. After birth, the newborn must rapidly open the lungs to clear the fetal lung liquid and establish a Functional Residual Capacity (FRC). There are two strategies to achieve this goal: Intermittent Positive Pressure Ventilation (IPPV) with positive end expiratory pressure (PEEP), and Sustained inflation (SI). It is not yet known which strategy is superior for lung aeration after birth. Further, performing non-invasive (i.e., facemask) respiratory support is technically difficult in preterm infants. The impact of common problems, such as facemask leak and airway obstruction, on the need for rescue endotracheal intubation is unknown. The objectives of this project are to (1) assess the effect of SI and IPPV on direct measures of lung aeration, and (2) to determine the impact of measured respiratory mechanics, such as mask leak, airway obstruction, and delivered tidal volumes, on need for rescue intubation in extremely preterm infants during delivery room resuscitation. To accomplish these objectives, this proposal will use a respiratory function monitor (RFM) to directly measure indicators of lung aeration in preterm infants during delivery room resuscitation. A RFM is a novel research tool that measures and displays respiratory characteristics of delivered inflations in real time. This project is an ancillary study of the SAIL trial (Sustained Aeration of Infant Lungs, Clinicaltrials.gov identifier NCT02139800), an ongoing international randomized controlled trial of SI versus IPPV as the initial lung aeration strategy in extremely preterm infants. RFM is an innovative tool to measure pulmonary mechanics during delivery room resuscitation. The SAIL trial will be the largest randomized trial of SI versus IPPV performed in extremely preterm infants to date. This project will take advantage of the existing SAIL trial framework and use RFM to identify the optimal approach to aerate the preterm lung after birth.